Arrangement for cathodic corrosion protection

ABSTRACT

A metallic element which is to be cathodically protected against corrosion has secured to one of its surfaces a strip-shaped anode extending along at least one generatrix and being in substantially continuous electrically conductive contact with such surface so that current will flow between the strip, which constitutes an anode, and the element, which constitutes a cathode, at substantially identical density all along the strip.

United States Patent [111 3,616,419

[72] Inventor Luigi Bagnulo 1 15,748 6/1971 Locke 204/ 148 Via Volta 18, Milan, Italy 1,254,344 l/l918 Murphy 204/148 [21] Appl. No. 713,551 1,871,125 8/1932 McGary et al.. 204/197 [22] Filed Mar. 15, 1968 2,011,613 8/1935 Brown et al..... 204/148 [45] Patented Oct. 26, 1971 2,303,778 12/1942 Wesley 204/197 [32] Priority Mar. 15, 1967 3,179,582 4/1965 Preiser 204/197 [33] Italy 3,202,596 8/1965 Canevari. 204/197 [31] 792945 3,260,661 7/1966 Kemp et a1... 204/148 3,332,867 7/1967 Miller et al.. 204/197 3,445,370 5/1969 Sherman 204/197 FOREIGN PATENTS EM N O C THOD C CORROS ON 39 25469 1 1/1964 Japan 204/197 PROTECHON Primary ExaminerT. Jung 1 1 Claims, 5 Drawing Figs. Attorney- Michael S. Striker [52] U.S. Cl 204/197,

72/368 ABSTRACT: A metallic element which is to be cathodically [51] Int. Cl C23 13/00 protected against corrosion has secured to one of its surfaces 3 [50] Field Of Search 204/147, strip-shaped anode extending along at least one generalrix and 1 1 197 being in substantially continuous electrically conductive contact with such surface so that current will flow between the [56] References Cited strip, which constitutes an anode, and the element, which con- UNITED STATES PATENTS stitutes a cathode, at substantially identical density all along 3,484,350 12/1969 Zaremski 204/197 the strip.

PATENTEUum 26 I9?! FIG 2 FIG:

FIG. 5

INVENTOR mum Gnu/aw ATTORN EY ARRANGEMENT FOR CATHODIC CORROSION PROTECTION BACKGROUND OF THE INVENTION It is well known that in the corrosion of metals local couples are formed on the corroding surface, some parts serving as anodes and therefore corroding and other parts sewing as cathodes and thus being protected. If, now, the whole surface is made cathodic to a separate anode and sufficient voltage is available between the two electrodes, then corrosion can be checked over the whole surface. It is to be understood, of course, that in order to obtain cathodic protection at least a minimum amount of current must flow from the anode to the cathode.

Cathodic protection can be achieved by two methods with the protective action obtained being the same in both cases. On the one hand a potential is generated by means of some metal or alloy having a greater solution pressure than the one which it is intended to protect. Two metals fonn a voltaic couple, the anode goes into solution and the cathode is protected against corrosion. On the other hand, a voltage from an external source may be applied to an anode and the surface to be protected serves as the cathode. In this latter case means for supplying direct current must of course be available.

The second approach is particularly known for the protection of metallic pipe lines carrying wet gases, water, or other corrosion-producing liquids, and for cables, vessels and the like which are similarly exposed to the danger of corrosion.

It is already known to provide cathodic protection under these circumstances through the use of so-calied "sacrificial" anodes spaced from one another in a given direction, for instances in the direction of elongation of a pipe which is to be protected. However, such spacing results in uneven current density along the surface which is to be protected so that such arrangements have been found to be less than satisfactory.

It is therefore a general object of the present invention to overcome these disadvantages.

SUMMARY OF THE INVENTION In accordance with one feature of my invention I provide an elongated metallic element having a surface exposed to a corrosion-producing fluid, and a metallic strip element extending on the surface in direction of elongation of the elongated element in substantially continuous electrically conductive contact therewith, the elongated metallic element constituting a cathode and the strip element constituting an anode with a direct current flowing from the latter to the former at substantially identical density along the entire elongation of the elements.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic end view of an arrangement embodying my invention;

FIG. 2 is a view similar to FIG. 1, but illustrating a different embodiment;

FIG. 3 is a fragmentary perspective view, illustrating one manner in which the anode may be secured to the cathode;

FIG. 4 is a view similar to FIG. 3, but illustrating a different manner of securing the anode to the cathode; and

FIG. 5 is a fragmentary side elevation showing still a further manner of securing the anode to the cathode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 of the drawing the member to be protected is illustrated as a metallic pipe P having an inner annular surface S to which there is secured, extending along at least one generatrix thereof, a strip-shaped metallic anode A. The force lines are shown by the dashed arrows.

In accordance with the present invention this anode A is intended to protect the pipe P against corrosion from corrosionproducing fluids flowing therethrough and acting as an electrolyte. The anode A is secured, also in accordance with the invention, in electrically conductive relationship to the surface S substantially continuously over its entire length. Securing can be effected by welding the anode A directly to the surface S, or by connecting-via partial embedding or the likean electrically conductive element with the anode A and in turn welding this element to the surface S of the pipe P.

In accordance with a further feature of my invention I may provide the surface S along the line over which the anode A is to be placed with a plurality of projections. This may be done by toughening the surface along this line, for instance by sandblasting or the like. Thereupon, a ribbon of adhesive material, such as resin material, mastic or the like, is placed along this line, care being taken that the free tips of whatever protrusions have been provided will penetrate the ribbon of adhesive material so that, when the anode A is placed onto the adhesive material to be held thereby on the surface S, these tips will be in electrically conductive engagement with the anode A. This latter construction avoids the formation of a film of fluid between the anode A and the surface S. The anode may consist of aluminum, zinc, magnesium or another alloy having a greater solutions pressure than the material of the pipe P and capable of forming with the metal of the pipe a voltaic couple. Under these circumstances a galvanic current will flow from the anode A to the pipe P and protect the latter cathodically. These considerations apply also, of course, if the anode A is placed on the exterior of the pipe P, for instance if the pipe is to be buried in the ground and is to be protected against corrosion resulting from the ambient moisture in the ground. It will be understood that it is imperative that there is a continuous or substantially continuous permanent metallic contact between the anode and whichever surface to which the anode is secured along the entire length of the surface, and that there be a direct contact between anode and surrounding fluid or, if the anode is on the exterior surface of a pipe which is to be buried in the ground, between the anode and the moisture-containing earth.

I have found it particularly advantageous to construct a pipe which is to be protected in this manner by affixing the anode to a metal sheet, for instance a steel sheet, which is subsequently formed into the desired tubular configuration. Affixing of the anode will, of course, be carried out in any of the various ways discussed above.

In providing a protective covering, for example a coating of paint, bitumen or another suitable compound, it is necessary to assure that the anode is not covered since this would destroy operativeness of the device. It is therefore advantageous to cover the anode prior to application of such coating with a protective and easily removable material, for instance an insulating adhesive tape which is removed subsequent to application of the coating, leaving the anode bare. Evidently this can be done regardless of whether the coating is carried out before or after the metallic sheet is formed into the desired tubular shape.

It will also be appreciated that it is possible to provide the anode not only on one surface, but on both surfaces with a tubular member, that is both the inner and the outer surface. Furthennore, it is of course clear that the invention is by no means limited to use with tubular members, inasmuch as it evidently can also be employed to protect cables or other metallic elements.

FIGS. 2-5 illustrate the different ways of positioning and securing the anode on the cathode which have been discussed above, and these FIGS. are therefore believed to be self-explanatory, it being clear that FIG. 2 illustrates the anode on the outer surface of the pipe, that FIG. 3 shows direct welding of the anode of the pipe while FIG. 4 shows securing of the anode by means of a partially embedded conductive strip which in turn is welded to the pipe, and that FIG. 5 shows adhesive securing of the anode to the pipe.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an arrangement for cathodic corrosion protection, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various. applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. An arrangement for cathodic corrosion protection comprising, in combination, an elongated tubular metallic element of predetermined length and having a surface of a predetermined area exposed to a corrosion-producing fluid; and a metallic strip element having a surface area which is substantially smaller than said predetermined area and extending on said surface in direction of elongation of said elongated element over the entire length of the latter in substantially continuous electrically conductive contact therewith, said elongated metallic elements constituting a cathode and said strip element consisting of a metal higher in the electromotive series than said metallic element and constituting an anode with a direct current flowing from said strip element to said metallic element at substantially identical density along the entire elongation of said elements for substantially uniform protection of said metallic element over said predetermined area of said exposed surface thereof.

2. An arrangement as defined in claim I, wherein said tubular element has inner and outer annular faces, and wherein said surface is constituted by one of said faces.

3. An arrangement as defined in claim 2, wherein said tubular element is a pipe adapted for passage therethrough of a corrosion-producing fluid, and wherein said surface is the inner annular face of said pipe.

4. An arrangement as defined in claim 2, wherein said surface is the outer face of said tubular element.

5. An arrangement as defined in claim 2, wherein said strip element extends along at least one continuous longitudinally extending strip-shaped portion of said surface.

6. An arrangement as defined in claim I, wherein said strip element is connected to said surface by a substantially continuous welded seam.

7. An arrangement as defined in claim 1; and further comprising an electrically conductive substance welded to said surface of said elongated metallic element and connected to said strip element.

8. An arrangement as defined in claim 1, wherein said surface comprises a plurality of protrusions arrayed longitudinally of said elongated metallic element; and further comprising a longitudinally extending ribbon of adhesive material interposed between said surface and said strip element substantially embedding said protrusion and having a thickness such that the tips of said protrusions project through said ribbon into electrically conductive contact with said strip element.

9. An arrangement as defined in claim overlying a strip portion of said surface; and further comprising a protective coating provided on and covering the remaining portion of said surface not covered by said strip element.

10. An arrangement as defined in claim 9, wherein said protective coating is paint.

11. An arrangement as defined in claim 9, tective coating is bitumen.

e e a a 1, said strip element wherein said pro- 

2. An arrangement as defined in claim 1, wherein said tubular element has inner and outer annular faces, and wherein said surface is constituted by one of said faces.
 3. An arrangement as defined in claim 2, wherein said tubular element is a pipe adapted for passage therethrough of a corrosion-producing fluid, and wherein said surface is the inner annular face of said pipe.
 4. An arrangement as defined in claim 2, wherein said surface is the outer face of said tubUlar element.
 5. An arrangement as defined in claim 2, wherein said strip element extends along at least one continuous longitudinally extending strip-shaped portion of said surface.
 6. An arrangement as defined in claim 1, wherein said strip element is connected to said surface by a substantially continuous welded seam.
 7. An arrangement as defined in claim 1; and further comprising an electrically conductive substance welded to said surface of said elongated metallic element and connected to said strip element.
 8. An arrangement as defined in claim 1, wherein said surface comprises a plurality of protrusions arrayed longitudinally of said elongated metallic element; and further comprising a longitudinally extending ribbon of adhesive material interposed between said surface and said strip element substantially embedding said protrusion and having a thickness such that the tips of said protrusions project through said ribbon into electrically conductive contact with said strip element.
 9. An arrangement as defined in claim 1, said strip element overlying a strip portion of said surface; and further comprising a protective coating provided on and covering the remaining portion of said surface not covered by said strip element.
 10. An arrangement as defined in claim 9, wherein said protective coating is paint.
 11. An arrangement as defined in claim 9, wherein said protective coating is bitumen. 